The present invention relates to sewing apparatus, and particularly to automatic sewing apparatus of the computerized type now gaining widespread use in the footwear and garment manufacturing industries.
Computerized sewing apparatus was introduced more than a decade ago. The currently-used apparatus generally includes X-Y servo systems having stepping motors and dedicated logic for controlling the movement of the workpiece along the X- and Y-coordinates, as well as for controlling the sewing head drive motor. One drawback generally present in the currently-used apparatus is that moving the workpiece along the X- and Y-coordinates does not always result in advancing it in the "legal" or "preferred" sewing direction. This may affect the quality of the sewing, particularly when certain types of stitching, such as top-stitching, is to be applied.
Another drawback is that the currently used systems generally require complex clamping devices for moving the workpieces with respect to the sewing head, and for retaining them in place during the sewing operations. Such clamping devices are quite costly and time-consuming to produce. Moreover, they require a loading operation which, if programmed in series with the sewing cycle, substantially increases the total production cycle time, and if programmed in parallel to the sewing cycle, substantially increases the cost by requiring the use of two or more similar clamps for every style or pattern to be sewn.
A further drawback in the current computerized sewing systems is that, although the sewing stitches can be applied very accurately by the sewing program, the workpiece itself is not always accurately cut so that the stitching applied to the workpiece may not present the best appearance. This is particularly true when the stitching is applied along the edge of the workpiece, as is frequently done in the garment and footwear industries.